The dissolution of alkali metal silicate glass to form solutions of sufficient concentration to have commercial value has long been recognized as the most difficult step in preparing such solutions. The first step in dissolving is an ion exchange between the alkali metal ions on the surface of the glass and hydrogen ions of the aqueous phase. The aqueous phase becomes alkaline and a layer of silanol groups is formed on the glass surface. The second stage of dissolving involves depolymerization and diffusion of the silicate ion into the bulk of the solution. To effect this depolymerization and diffusion, water and ions must penetrate the glass. However, the silanol groups formed by the ion exchange step resemble a polymer in their protective resistance to penetration and diffusion. As a consequence of such behavior silanol groups, silicate ions and water are retained on the glass surface as a semisolid. Until now, high temperatures and pressures as well as excess glass and prolonged dissolving times have been necessary to produce silicate solutions of commercial value. The use of such extreme conditions produces solutions that are cloudy and must be filtered or settled for long periods of time to attain a clear solution. Dissolving and treating of silicate glass in ball mills and the like to achieve faster dissolution has been suggested; however, these solutions are quite turbid and usually contain impurities from the mill.
I have found that if the protective layer consisting of silanol groups, silicate ions and water can be continuously removed and diffused away from the glass surface constantly exposing nascent glass surfaces, alkali metal silicate solutions of commercial concentration can be formed after short dissolving times, at temperatures below the boiling points of water or of the silicate solutions formed and at atmospheric pressure. The resulting solutions are clear and need not be filtered or settled.